1. Field of the Invention
This invention relates to wavelength conversion methods and light source devices using the same. Such light sources are useful in lighting and projection system.
2. Description of the Related Art
An important aspect of light source technology development is enhancing the output brightness and power simultaneity. Taking as examples light sources for projection devices, headlights or illuminating lamps for transport devices such as vehicles, motorcycles, boats or airplanes, searchlight etc., conventional light sources use ultra high power (UHP) lamps for providing white light. A color conversion device such as multi-segmented color wheels are used to generate desired red, green and blue light.
With the development in solid-state light sources, in particular light emitting diode (LED), light source systems increasingly adopt solid-state light source as a light emitting source, to overcome the shortcomings of UHP lamps such as high driving voltage, and long waiting time when turning on/off. Other benefits of solid-state light sources include improved color effect of monochromatic light, enhanced color gamut, extended life of the light source system, and reduced power consummation.
An LED light source system typically uses a monochromatic LED and a wavelength conversion device having wavelength conversion materials to generate various colored light. The wavelength conversion materials may include phosphors, quantum dots, fluorescent dyes, nano light emitting materials, etc. The light conversion device may employ, for example, a color wheel that carries one or more types of phosphors. The excitation light produced by the LED is introduced onto the rotating color wheel, and the different wavelength conversion materials generate converted light of different colors. For example, in a typical three primary colors projection system, a blue light produced by a LED light source is introduced onto the rotating color wheel with multiple segments carrying a different wavelength conversion material to generate red, green, blue light sequentially.
When the phosphor absorbs an excitation light, it emits a converted light with a Lambertian distribution in all directions. To improve efficiency in a wavelength conversion device 10, as shown in FIG. 1, a first filter 101A is provided on one side of the phosphor layer 102 (carried on a color wheel) for transmitting the excitation light and reflecting the converted light emitted by phosphor. Further, a second filter 103A is provided on the other side of the phosphor layer 102 for adjusting the light spectrum or the output angle of the output light. The second filter may have different segments with optical characters such as high-pass, low-pass, band-pass etc. that correspond to the converted light from different segments of the color wheel.
However, the cost of the filter, especially the first filter, is high. The cost of the filters can be about 60 percent to 80 percent of the total cost of the light conversion device.